Experts think there may also be many people with no symptoms at all, or such mild ones that they never bother to seek medical attention. Because those cases have not been counted, it’s not possible now to know the real proportion of mild versus severe cases.
Antibody tests, which can determine whether someone has ever been infected, may eventually help to establish how many people had mild or asymptomatic coronavirus infections.
After viral infections, people generally develop antibodies in their blood that will fight off the virus and protect them from contracting it again. It’s reasonable to assume that people who have had the new coronavirus will become immune to it.
But it is not known how long that immunity will last. With other coronaviruses, which cause the common cold, immunity can wane.